A method for making silica gel having a large active surface area is known in which a sodium silicate solution with a specific gravity of 1.10 and a sulfuric acid solution with a specific gravity of 1.20 are mixed at a ratio of 100 to 15 parts by volume, the sulfuric acid solution being poured into the sodium silicate solution. The gelled mass thus produced is aged at a temperature of 20.degree. C. to 25.degree. C. for 24 hours, then is dried at a temperature of 30.degree. C. to 40.degree. C. The gelled mass is, subsequently, treated with 3% sulfuric acid solution, is washed several times with distilled water, and is aged again at a temperature of up to 100.degree. C.
A disadvantage of the method is the impossibility of making silica gel having a sufficiently large active surface area and, at the same time, a microgranular structure. The product of the known method includes comparatively large aggregates of particles. The particles contain amorphous fragments that require additional crushing. Such additional crushing is often undesirable because it is associated with product contamination.
A method of making silica gel having a large active surface area is also known, in which a sodium silicate solution containing 9.9% to 21.4% by mass of silicon dioxide is added to 3.6 to 9.3 normal sulfuric acid solution at a volume ratio of 4 or 5 to 1 and the resulting gel mass is aged at room temperature or at a temperature of 60.degree. C. for 45 to 120 minutes. The gelled mass is then washed with 0.2 normal sulfuric acid solution and, finally, is dried at 200.degree. C.
Disadvantages of the method are the usage of high concentration initial reagents that require mixers of special types in order to produce a sufficiently homogenized gel mass, the necessity of crushing the final product by means of a crushing apparatus, and the production of silica gel having comparatively small pore volume. Relatively low pore volume makes the use of the product as an adsorbent-separator in hermetically sealed acid accumulators difficult.
An object of the invention is the provision of a method for making silica gel having a large active surface area and, at the same time, a microgranular structure. The method should produce aggregate particles of small size that require no additional grinding and that have large pore volume. Furthermore, the method should utilize initial reagents with comparatively low concentrations and avoid the use of mixers of special types.